My 16-year-old nephew has a big problem with my sister’s new partner. The Guardian.

My nephew is 16 and studying for his A-levels. My sister and her husband have been separated for four years and my nephew spends three nights per week with his father. My nephew appears to have a big problem with my sister’s partner, who has recently moved in (they have had a relationship for two and a half years). He is a mature man with adult children of his own with whom he has a good relationship; he is a reasonable, sociable person. Since he moved in, my nephew refuses to come out of his bedroom and will only communicate with his mother by text or shouting from his room. If they meet face to face, he is verbally aggressive.

My sister has tried to convince him that she will always love him, and that her partner will not try to become a new “father”, telling him what to do (a worry my nephew expressed). This has gone on for over a month and she is at the end of her tether.

My nephew has, in my view, always been mollycoddled, and until recently hung around his mother in a way that I would have been embarrassed to do.

He is afraid of his father and will not tell him that he does not want to spend three nights a week with him. His older sisters do not communicate with their father as he can be verbally abusive.

My partner and I are in our 60s and willing to try to talk things through with my nephew in a civilised manner to try to sort out the situation, but would, if necessary, point out in no uncertain terms that he is behaving like a spoilt six-year-old and that his behaviour is unacceptable.

Do you think us reading him the riot act would snap him out of his semi-hysterical behaviour pattern?

Let’s stop and look at things from the boy’s point of view. He may look like a man but, inside, he is still very young. His parents have split up and he is forced to go and stay with his dad, a man of whom he sounds afraid – for three nights a week. There has been no man in the house for years, until a month ago. And he’s studying for his A-levels. That’s a lot to be getting on with.

Should you read him the riot act? No. This is a brilliant opportunity for you to step up and show him the patience and understanding you expect him to have. This is a chance for you to be a man he can look up to – not to be yet another person telling him what to do.

I talked to Rachel Melville-Thomas, a child and adolescent psychotherapist (childpsychotherapy.org.uk). She sees many young people like your nephew. “This is about an adolescent trying to get to grips with a blended family,” she said. “And a month is no time at all – all the research says it takes one to two years. So don’t expect it to be instant.”

You seem to think that talking to the boy once is enough to change things. It isn’t. You need to show patience and understanding. Why are you so angry with him? I sometimes think we show anger to family members we can, rather than those we are actually angry with.

Melville-Thomas explained that the commonest teenage worries are largely to do with who they are, where they belong, what they look like and who they are going to be when they are not their parents’ child. She said: “At the moment, your nephew doesn’t know how to be a reasonable man or who should be his role model: his father, who is verbally aggressive or his new stepfather.”

When teenagers withdraw, it’s usually due to several things, and their anger usually masks fear, sadness and anxiety. Your nephew is probably terrified. “I’ve seen this so many times,” said Melville-Thomas, “a child or adolescent not adapting fast enough to an adult situation. They won’t say ‘I’m really worried’ – they act out. The adult says, ‘What this person needs is a firm hand’ – actually, the child needs to be understood.”

We thought that the boy’s mother needed to ask him how he feels, something like: “It’s a funny time, isn’t it – it was you and me, and now X is here. How is that for you? How would you like it to be now he’s here?” The boy may well need one-to-one time with his mother.

Take it slowly. This boy isn’t a machine. You’d give a stranger in the street more help and guidance than you are currently giving your nephew.

Here are a few outside resources for you and your sister to read: Familylives.org.uk has some great reading about step families, and a book called Raising Boys by Steve Biddulph, published by Harper Thorsons.

This article first appeared in The Guardian Family section on 17 January 2015.